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Area Forecast Discussion
144 FXUS64 KHUN 280259 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 959 PM CDT MON JUN 27 2016 .UPDATE... Evening update to public forecast. && .DISCUSSION... Latest radar data suggests that coverage of residual light rain in the wake of afternoon convection continues to dissipate this evening, and POPs will be lowered for majority of the region for the remainder of the night. That said, we will need to closely monitor the progress of a small backward propagating MCS currently across northern portions of the Cumberland Plateau in TN. Short term models suggest that sfc-850 mb flow will gradually veer throughout the night a 500-mb trough axis advances southeastward through the region, and this may be sufficient to sustain this MCS for several more hours. Although bulk of the convection will likely remain to the east of our forecast area, we will maintain a slightly higher prob for both showers and thunderstorms in ne Alabama and southern TN. Weak ascent associated with the 500-mb trough may be sufficient for a few sprinkles or patches of light rain in remainder of the region, and a 20% POP will be included for rest of the forecast area. Otherwise, a nearly saturated boundary layer and light flow regime will be favorable for more widespread fog formation early Tuesday morning, with areas of fog possible. Visibility should be confined to the 3-5 mile range, however, due to impacts from a lingering deck of altostratus clouds. Temps/dewpoints and winds look good with no changes required. 70/DD && .AVIATION... (Issued 706 PM CDT MON JUN 27 2016) For 00Z TAFs: Although primary axis of tsra has now shifted well to the se of MSL/HSV, residual -ra will continue at each terminal for a few hrs early this evening. This should not have a significant impact on airport operations with vsbys expected to remain aoa 6 sm and cigs expected to be aoa 7 kft, but we did include -ra as prevailing wx cond thru 28/04Z. Ovc altostratus layer will persist for remainder of the night, but still expect fairly widespread br/fg to develop shortly after pcpn ends arnd 04Z. Prevailing vsbys should remain in the 3-5 sm range, with periodic drops to arnd 2 sm btwn 07-11Z. Conds will improve after 13-14Z as nne flow strengthens and drier air pushes into the region. Higher probs for storms tomorrow will be south of the TN River, so we will include no pcpn in either TAF attm. 70/DD && .PREV DISCUSSION... (Issued 706 PM CDT MON JUN 27 2016) (Issued 223 PM CDT MON JUN 27 2016) At 19z, showers and thunderstorms were continuing to develop and overspread the forecast area from the west and northwest along and ahead of a convergent boundary/pre-frontal trough. This boundary was extending southwest out of middle Tennessee into north Mississippi. Dewpoint temps ahead of the storms had increased into the low-mid 70s except for northeast Alabama, where the lower atmosphere had mixed out a bit with dewpoint temps there in the upper 60s. Will continue into the evening with likely to occasional shra/tsra and will slowly lessen pops with time into the overnight hours as the RAP/HRRR and Hi-Res short term models indicate that there should be some subsidence that will move southeast into the area behind the initial band of shra/tsra across the area. The short term models are indicative that the main cold front should shift southeast into middle Tennessee by 12z Tuesday and through the southern portions of the forecast area by 18z Tuesday. Will maintain low chance pops for Tuesday due to the proximity of the cold front to the forecast area. Expecting that afternoon heating/instability and still decent PWAT values above an inch, should contribute to at least low chance pops across the region. The cold front is progged by the models to be well south of the forecast area by Tuesday night with high pressure building southeast out of the midwest toward the Tennessee valley. A mid to upper level northwest flow aloft will result in dry and cooler weather for the forecast area through Thursday. Both the GFS and ECMWF models are in similar agreement involving the southeast movement of the next cold front through the midwest. The upper flow is expected to become also more zonal by Friday as a short wave is expected to move slowly east-southeast through the southern plains along the frontal boundary. Will slowly increase pops into the chance category by Saturday as the frontal boundary and short wave get a little closer to the forecast area. By Saturday, the ECMWF model indicated that the frontal boundary should stall out over middle Tennessee, while the GFS model characteristically indicated that the cold front would make it into north Alabama. Will follow closer to the more conservative ECMWF model involving the frontal placement. The nearly stationary cold front is expected to slowly shift southward to close to the forecast area by Sunday and have gone with higher chance pops from Sunday through Monday. As far as temps are concerned, will trend more toward the slightly cooler GFS temps through the extended forecast periods. TT && .HUN Watches/Warnings/Advisories... AL...NONE. TN...NONE. && $$ For more information please visit our website at weather.gov/huntsville.